The present invention relates to a process for producing alkylaromatics, particularly ethylbenzene and cumene.
Ethylbenzene and cumene are valuable commodity chemicals which are used industrially for the production of styrene monomer and phenol respectively. Ethylbenzene may be produced by a number of different chemical processes but one process which has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. In the commercial operation of this process, the polyalkylated benzenes, including both polymethylated and polyethylated benzenes, which are inherently co-produced with ethylbenzene in the alkylation reactor, are transalkylated with benzene to produce additional ethylbenzene either by being recycled to the alkylation reactor or by being fed to a separate transalkylation reactor. Examples of such ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge), and U.S. Pat. No. 4,016,218 (Haag).
More recently focus has been directed at liquid phase processes for producing ethylbenzene from benzene and ethylene since liquid phase processes operate at a lower temperature than their vapor phase counterparts and hence tend to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 describes the liquid phase synthesis of ethylbenzene with zeolite beta, whereas U.S. Pat. No. 5,334,795 describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene.
Cumene has for many years been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. More recently, however, zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
U.S. Pat. No. 5,453,554 describes a process for producing short chain alkyl aromatic compounds, such as cumene and ethylbenzene, by contacting at least one alkylatable aromatic compound, such as benzene, with an alkylating agent having 1–5 carbon atoms in the presence of MCM-56. The process can be effected in either the liquid or vapor phase and polyalkyated by-products can be converted to additional monoalkylated product by transalkylation in the alkylation reactor or in a separate reactor. According to the '554 patent, the transalkylation catalyst can be MCM-49, MCM-22, PSH-3, SSZ-25, zeolite X, zeolite Y, zeolite beta or mordenite. Particular forms of mordenite cited in the '554 patent as suitable transalkylation catalysts are acid-dealuminized mordenite as disclosed in U.S. Pat. No. 5,243,116 and TEA-mordenite as disclosed in U.S. Pat. Nos. 3,766,093 and 3,894,104. Although U.S. Pat. Nos. 3,766,093 and 3,894,104 are silent as to the crystal size of the TEA-mordenite produced therein, a repeat of the Examples in these patents has shown the mordenite product to be predominantly large crystals with a size greater than 1 micron and typically around 5 to 10 micron.
One problem which exists in liquid phase processes for producing alkylaromatics, such as cumene and ethylbenzene, is that their lower operating temperatures increases the activity requirements of the catalyst particularly in the transalkylation step and an object of this invention is to provide an aromatics transalkylation catalyst of enhanced activity.
In particular, it has now unexpectedly been found that by producing TEA-mordenite with a controlled small crystal size of less than 0.5 micron, it is possible to produce a catalyst with materially enhanced activity for liquid phase aromatics transalkylation.